U.S. patent application number 14/640886 was filed with the patent office on 2015-09-17 for mems device and method of manufacturing the same.
The applicant listed for this patent is SEIKO EPSON CORPORATION. Invention is credited to Takahiko YOSHIZAWA.
Application Number | 20150259193 14/640886 |
Document ID | / |
Family ID | 54068172 |
Filed Date | 2015-09-17 |
United States Patent
Application |
20150259193 |
Kind Code |
A1 |
YOSHIZAWA; Takahiko |
September 17, 2015 |
MEMS DEVICE AND METHOD OF MANUFACTURING THE SAME
Abstract
A present MEMS device includes: a functional element with a
connection electrode; a structural member that forms a cavity
surrounding the functional element; a second insulating film
provided so as to surround a predetermined region on a first
surface of the connection electrode; a first lid portion that has a
third insulating film, is provided with an opening, and covers a
part of the cavity; a second lid portion that has a first
conductive member and a sealing portion, the first conductive
member being electrically connected to the predetermined region of
the connection electrode, and the sealing portion sealing the
opening of the first lid portion; a fourth insulating film that
insulates the first conductive member from the sealing portion; and
a second conductive member that penetrates the fourth insulating
film and is electrically connected to the first conductive
member.
Inventors: |
YOSHIZAWA; Takahiko;
(Sakata-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEIKO EPSON CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
54068172 |
Appl. No.: |
14/640886 |
Filed: |
March 6, 2015 |
Current U.S.
Class: |
257/415 ;
438/51 |
Current CPC
Class: |
B81B 2207/015 20130101;
B81B 7/007 20130101 |
International
Class: |
B81B 7/00 20060101
B81B007/00; B81C 1/00 20060101 B81C001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2014 |
JP |
2014-048448 |
Claims
1. A MEMS device, comprising: a substrate; a functional element
that is provided, either directly or via a first insulating film,
on a surface of the substrate, and includes a connection electrode;
a structural member that is provided on the surface of the
substrate or on a surface of the first insulating film, and forms a
cavity surrounding the functional element; a second insulating film
that is provided so as to surround a predetermined region on a
first surface of the connection electrode; a first lid portion that
includes a third insulating film covering the second insulating
film at the first surface of the connection electrode, is provided
with an opening, and covers a part of the cavity; a second lid
portion that is provided on a surface of the first lid portion and
includes a first conductive member and a sealing portion, the first
conductive member being electrically connected to the predetermined
region of the connection electrode, and the sealing portion sealing
the opening of the first lid portion; a fourth insulating film that
is provided on a surface of the second lid portion, is in contact
with the second insulating film or the third insulating film, and
insulates the first conductive member from the sealing portion; and
a second conductive member that penetrates the fourth insulating
film and is electrically connected to the first conductive
member.
2. The MEMS device according to claim 1, wherein the fourth
insulating film penetrates the second lid portion and the third
insulating film and is in contact with the second insulating
film.
3. The MEMS device according to claim 1, wherein the substrate is a
semiconductor substrate provided with a semiconductor circuit
element, and a contact plug that penetrates at least the fourth
insulating film and is electrically connected to the semiconductor
circuit element is provided, and the second conductive member that
is electrically connected to the first conductive member is formed
of the same material as the contact plug.
4. The MEMS device according to claim 3, wherein the cavity is
formed in a trench of the semiconductor substrate.
5. The MEMS device according to claim 1, wherein the second
insulating film and the fourth insulating film are formed of
silicon dioxide (SiO.sub.2), the third insulating film is formed of
silicon nitride (SiN), and the second lid portion is formed of
aluminum (Al).
6. The MEMS device according to claim 3, wherein the contact plug
is formed of tungsten (W).
7. A method of manufacturing a MEMS device, the method comprising:
(a) forming a functional element and a structural member, either
directly or via a first insulating film, on a surface of a
substrate, the functional element including a connection electrode,
and the structural member forming a cavity surrounding the
functional element; (b) forming a second insulating film such that
the second insulating film surrounds a predetermined region on a
first surface of the connection electrode and is present in the
cavity; (c) forming a first lid portion which includes a third
insulating film covering the second insulating film at the first
surface of the connection electrode, in which an opening is formed,
and which covers a part of the cavity; (d) removing the second
insulating film in the cavity through release etching; (e) forming
a second lid portion on a surface of the first lid portion in a
vacuum chamber, the second lid portion including a first conductive
member and a sealing portion, the first conductive member being
electrically connected to the predetermined region of the
connection electrode, and the sealing portion sealing the opening
of the first lid portion; (f) forming, on a surface of the second
lid portion, a fourth insulating film that is in contact with the
second insulating film or the third insulating film and insulates
the first conductive member from the sealing portion; and (g)
forming a second conductive member that penetrates the fourth
insulating film and is electrically connected to the first
conductive member.
8. The method of manufacturing the MEMS device according to claim
7, wherein (b) includes forming the second insulating film with
silicon dioxide (SiO.sub.2), (c) includes forming the third
insulating film with silicon nitride (SiN), (e) includes forming
the second lid portion with aluminum (Al), and (f) includes forming
the fourth insulating film with silicon dioxide (SiO.sub.2).
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to, for example, a MEMS (Micro
Electro Mechanical Systems) device in which a functional element,
such as a resonator, a sensor and an actuator, and/or an electronic
circuit are integrated on one substrate, and a method of
manufacturing such a MEMS device.
[0003] 2. Related Art
[0004] For example, in a MEMS device that includes a resonator with
capacitance as a functional element, the resonator is airtightly
sealed, in a vacuum state, in a cavity formed in a substrate.
Therefore, a cavity is formed by providing the substrate with a
structural member that surrounds the resonator, and a lid portion
(cap layer) is joined to the cavity with the inside of the cavity
placed in a vacuum state.
[0005] Traditionally, an insulating substance of silicon nitride
(P--SiN) and the like deposited using a plasma CVD (Chemical Vapor
Deposition) technique is used as the lid portion for the cavity.
However, in a case where the insulating substance of silicon
nitride and the like is used as the lid portion for the cavity,
high-vacuum cavity sealing required in a high-performance MEMS
device cannot be realized.
[0006] Also, aluminum (Al), which is a material of wiring connected
to impurity diffusion regions of a MOS field-effect transistor and
the like, doubles as a material of a conductive member electrically
connected to an external connection electrode of a functional
element. However, in the case of a high-performance MOS
field-effect transistor, a contact plug of tungsten (W) is used as
a connecting member instead of the wiring of aluminum (Al).
Therefore, a material of the connecting member for the functional
element cannot double as a material of the connecting member for
the high-performance MOS field-effect transistor.
[0007] As related art, the specification of U.S. Pat. No. 5,798,283
(columns 7 and 8, FIGS. 8 and 9) discloses MEM devices with an
electronic circuitry on a common substrate. A cavity is formed in a
substrate of these MEM devices, and silicon nitride (SiN) or
silicon dioxide (SiO.sub.2) is used as a material of a lid portion
(cap layer) for the cavity.
[0008] On the other hand, JP-A-2009-272477 (paragraphs 0020 to
0027, FIG. 1) discloses a MEMS sensor in which a cavity is formed
by a structural member provided on a semiconductor substrate. In
this MEMS sensor, a wall portion of the cavity is provided on a
silicon substrate via an insulating layer of silicon oxide and the
like, and a peripheral portion of a lid portion (cap) for the
cavity is supported on the wall portion of the cavity via the
insulating layer of silicon oxide and the like. Here, the cap, a
ground conductive portion, and a voltage application conductive
portion are made of doped polysilicon and are formed on the same
layer.
[0009] The specification of U.S. Pat. No. 5,798,283 (columns 7 and
8, FIGS. 8 and 9) and JP-A-2009-272477 (paragraphs 0020 to 0027,
FIG. 1) are examples of related art.
[0010] According to the specification of U.S. Pat. No. 5,798,283
(columns 7 and 8, FIGS. 8 and 9), as silicon nitride (SiN) or
silicon dioxide (SiO.sub.2) is used as a material of the lid
portion for the cavity, it is difficult to realize high-vacuum
cavity sealing. On the other hand, in JP-A-2009-272477 (paragraphs
0020 to 0027, FIG. 1) that uses polysilicon with electrical
conductivity as a material of the lid portion for the cavity, it is
necessary to positionally align and join a side wall of the cavity
and the lid portion with/to each other in a vacuum chamber. In
addition, a structure for insulating and isolating a wiring portion
for a functional element and the lid portion for the cavity from
each other is important.
SUMMARY
[0011] A first advantage of some aspects of the invention is that,
in a MEMS device with a cavity in which a functional element is
provided, high-vacuum cavity sealing required in a high-performance
MEMS device is realized using a relatively simple structure and
manufacturing method. A second advantage of some aspects of the
invention is that a wiring portion for the functional element and a
lid portion for the cavity are reliably insulated and isolated from
each other. A third advantage of some aspects of the invention is
that a material of a connecting member for the functional element
doubles as a material of a connecting member for a high-performance
semiconductor circuit element.
[0012] A MEMS device according to an aspect of the invention
includes: a substrate; a functional element that is provided,
either directly or via a first insulating film, on a surface of the
substrate, and has a connection electrode; a structural member that
is provided on the surface of the substrate or on a surface of the
first insulating film, and forms a cavity surrounding the
functional element; a second insulating film that is provided so as
to surround a predetermined region on a first surface of the
connection electrode; a first lid portion that has a third
insulating film covering the second insulating film at the first
surface of the connection electrode, is provided with an opening,
and covers a part of the cavity; a second lid portion that is
provided on a surface of the first lid portion and has a first
conductive member and a sealing portion, the first conductive
member being electrically connected to the predetermined region of
the connection electrode, and the sealing portion sealing the
opening of the first lid portion; a fourth insulating film that is
provided on a surface of the second lid portion, is in contact with
the second insulating film or the third insulating film, and
insulates the first conductive member from the sealing portion; and
a second conductive member that penetrates the fourth insulating
film and is electrically connected to the first conductive
member.
[0013] A method of manufacturing a MEMS device according to an
aspect of the invention includes: (a) forming a functional element
and a structural member, either directly or via a first insulating
film, on a surface of a substrate, the functional element having a
connection electrode, and the structural member forming a cavity
surrounding the functional element; (b) forming a second insulating
film such that the second insulating film surrounds a predetermined
region on a first surface of the connection electrode and is
present in the cavity; (c) forming a first lid portion which has a
third insulating film covering the second insulating film at the
first surface of the connection electrode, in which an opening is
formed, and which covers a part of the cavity; (d) removing the
second insulating film in the cavity through release etching; (e)
forming a second lid portion on a surface of the first lid portion
in a vacuum chamber, the second lid portion having a first
conductive member and a sealing portion, the first conductive
member being electrically connected to the predetermined region of
the connection electrode, and the sealing portion sealing the
opening of the first lid portion; (f) forming, on a surface of the
second lid portion, a fourth insulating film that is in contact
with the second insulating film or the third insulating film and
insulates the first conductive member from the sealing portion; and
(g) forming a second conductive member that penetrates the fourth
insulating film and is electrically connected to the first
conductive member.
[0014] According to an aspect of the invention, the second lid
portion, which includes the first conductive member electrically
connected to the connection electrode of the functional element and
the sealing portion sealing the opening of the first lid portion,
is provided on the surface of the first lid portion. Therefore,
high-vacuum cavity sealing required in a high-performance MEMS
device can be realized using a relatively simple structure and
manufacturing method. Also, as a material of the first conductive
member electrically connected to the connection electrode of the
functional element doubles as a material of the sealing portion,
manufacturing processes of the MEMS device can be reduced.
[0015] Here, the fourth insulating film may penetrate the second
lid portion and the third insulating film and be in contact with
the second insulating film. In this way, the first conductive
member and the sealing portion can be reliably insulated and
isolated from each other by the second to fourth insulating
films.
[0016] Also, the substrate may be a semiconductor substrate
provided with a semiconductor circuit element, a contact plug that
penetrates at least the fourth insulating film and is electrically
connected to the semiconductor circuit element may be provided, and
the second conductive member that is electrically connected to the
first conductive member may be formed of the same material as the
contact plug. In this way, a material of a connecting member for
the functional element can double as a material of a connecting
member for the semiconductor circuit element.
[0017] In this case, the cavity may be formed in a trench of the
semiconductor substrate. In this way, a layer structure formed on
the semiconductor substrate is planarized, and formation of a
wiring layer is made easy. In addition, the height of an upper end
of a contact plug for the functional element can be aligned with
the height of an upper end of a contact plug for the semiconductor
circuit element, and these contact plugs can be brought into
connection to each other by wiring provided on the same layer.
[0018] The above-referenced second and fourth insulating films,
third insulating film, and second lid portion may be formed of
silicon dioxide (SiO.sub.2), silicon nitride (SiN), and aluminum
(Al), respectively. In this case, in a release etching process, the
second insulating film of silicon dioxide can be protected by the
third insulating film of silicon nitride that has a high resistance
to an etchant, and a degree of vacuum can be prevented from
decreasing due to discharge of gas, such as water vapor, from
silicon dioxide. Also, aluminum is suitable as a material of the
sealing portion that realizes high-vacuum cavity sealing required
in a high-performance MEMS device.
[0019] Furthermore, the contact plug may be formed of tungsten (W).
In the case of a high-performance MOS field-effect transistor, a
contact plug of tungsten (W) is used as a connecting member.
Therefore, by forming the second conductive member that is
electrically connected to the first conductive member with tungsten
(W), a material of a connecting member for the functional element
can double as a material of a connecting member for the
high-performance MOS field-effect transistor.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0021] FIG. 1 is a cross-sectional view showing major portions of a
MEMS device according to an embodiment of the invention.
[0022] FIGS. 2A to 2C are cross-sectional views pertaining to
manufacturing processes of the MEMS device according to the
embodiment of the invention.
[0023] FIGS. 3A to 3C are cross-sectional views pertaining to
manufacturing processes of the MEMS device according to the
embodiment of the invention.
[0024] FIGS. 4A and 4B are enlarged cross-sectional views showing a
part of the MEMS device in major manufacturing processes.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0025] The following describes an embodiment of the invention in
detail with reference to the accompanying drawings. It should be
noted that the same constituent element is assigned the same
reference sign, and redundant descriptions are omitted.
[0026] A MEMS device according to the embodiment of the invention
is a device in which a functional element, such as a resonator, a
sensor and an actuator, and/or an electronic circuit are integrated
on one substrate.
[0027] Below, as one example, a MEMS device will be described that
includes a resonator with capacitance as a functional element, and
also includes a MOS field-effect transistor as a semiconductor
circuit element. The resonator is, for example, airtightly sealed
in a cavity formed in a trench (a recessed portion in a surface) of
a semiconductor substrate.
[0028] FIG. 1 is a cross-sectional view showing major portions of
the MEMS device according to the embodiment of the invention. As
shown in FIG. 1, this MEMS device uses a semiconductor substrate 10
whose main surface (an upper surface in the figure) has a first
region (the right side in the figure) in which a trench is formed
and a second region (the left side in the figure) in which impurity
diffusion regions of a semiconductor circuit element are
formed.
[0029] The resonator includes a lower electrode 31, an upper
electrode 32 and an external connection electrode 33 that are
provided on a bottom surface of the trench of the semiconductor
substrate 10 via an insulating film 20. A wall portion 34 is
provided as a structural member that forms a cavity surrounding
these electrodes. For example, the insulating film 20 includes an
insulating film 21 of silicon dioxide (SiO.sub.2) and an insulating
film 22 of silicon nitride (SiN). It should be noted that the wall
portion 34 may be provided directly on the bottom surface of the
trench of the semiconductor substrate 10. Also, in a case where a
substrate with high insulating properties, such as a substrate of
glass, ceramics, resin, or the like, is used, the lower electrode
31 to the external connection electrode 33 may be provided directly
on the substrate.
[0030] The lower electrode 31 to the wall portion 34 are formed of,
for example, polysilicon that has been doped with impurities and
has electrical conductivity. The upper electrode 32 of the
resonator includes a cantilever-like structural member that is
fixed at one end and movable at the other end. The external
connection electrode 33 is electrically connected to the lower
electrode 31, and may be constructed integrally with the lower
electrode 31. It should be noted that, in FIG. 1, an external
connection electrode that is electrically connected to the upper
electrode 32 is not shown.
[0031] In the trench of the semiconductor substrate 10, a region
surrounded by the wall portion 34 is the cavity. The space in the
cavity is a high-vacuum region. By applying an alternating current
voltage between the lower electrode 31 and the upper electrode 32
in the resonator provided in the cavity, mechanical oscillation of
the upper electrode 32 is excited by an electrostatic force, and a
change in capacitance between the lower electrode 31 and the upper
electrode 32 attributed to this mechanical oscillation is
detected.
[0032] The external connection electrode 33 has, for example, a
shape of a flat prism or cylinder, and an insulating film 41 is
provided so as to surround a predetermined region on a first
surface (an upper surface in the figure) of the external connection
electrode 33. At the first surface of the external connection
electrode 33, an insulating film 51 that covers the insulating film
41 is also provided.
[0033] Here, it is easy to increase a film thickness of the
insulating film 41, and the insulating film 51 has a higher
resistance to an etchant than the insulating film 41 in a
later-described release etching process. For example, the
insulating film 41 may be formed of silicon dioxide (SiO.sub.2) and
the like, and the insulating film 51 may be formed of silicon
nitride (SiN) and the like.
[0034] Together with a polysilicon film 52 that has electrical
conductivity, the insulating film 51 constitutes a first lid
portion 50. It should be noted that a surface of the polysilicon
film 52 may be provided with a titanium nitride (TiN) film, a
salicide film, or the like. Also, a part of the polysilicon film 52
is provided in the predetermined region of the first surface of the
external connection electrode 33, and is electrically connected to
the external connection electrode 33. An opening (release hole) 50a
is formed in the first lid portion 50. The part of the first lid
portion 50 other than the opening 50a covers the cavity.
[0035] With the inside of the cavity placed in a decompressed state
(vacuum state), a second lid portion 60 is formed on a surface of
the first lid portion 50 by metal, such as aluminum (Al). It should
be noted that this surface of the first lid portion 50 and a
cavity-side face of the first lid portion 50 represent front and
back faces. The second lid portion 60 includes an intermediate
conductive member 61 that is electrically connected to the
predetermined region of the first surface of the external
connection electrode 33 via the polysilicon film 52, and a sealing
portion 62 that seals the opening 50a of the first lid portion.
[0036] In this way, the second lid portion 60, which includes the
intermediate conductive member 61 electrically connected to the
external connection electrode 33 of the resonator and the sealing
portion 62 that seals the opening 50a of the first lid portion, is
provided on the surface of the first lid portion 50. Accordingly,
high-vacuum cavity sealing required in a high-performance MEMS
device can be realized using a relatively simple structure and
manufacturing method.
[0037] An insulating film 70 of silicon dioxide (SiO.sub.2), BPSG
(Boron Phosphorus Silicon Glass), or the like is provided on a
surface of the second lid portion 60. The insulating film 70 is in
contact with the insulating film 41 or 51, and insulates the
intermediate conductive member 61 from the sealing portion 62. The
insulating film 70 may constitute an insulating/isolating portion
by penetrating the second lid portion 60 and the insulating film 51
and coming into contact with the insulating film 41 as shown in
FIG. 1. In this way, the insulating film 41, the insulating film 51
and the insulating film 70 can reliably insulate and isolate the
intermediate conductive member 61 from the sealing portion 62.
[0038] The insulating film. 70 may extend to a second region of the
semiconductor substrate 10 in which the semiconductor circuit
element is formed. The semiconductor circuit element is provided in
the second region of the semiconductor substrate 10. For example,
impurity diffusion regions 81 and 82, which serve as a source and a
drain of a MOS field-effect transistor (MOSFET), are provided
inside the semiconductor substrate 10, and a gate electrode 83 is
provided on the semiconductor substrate 10 via a gate insulating
film. Also, for example, a contact plug (electrode) 91 of tungsten
(W) and the like, which penetrates at least the insulating film 70
and is electrically connected to the impurity diffusion regions 81
and 82 and the gate electrode 83, is provided.
[0039] Therefore, in a first region of the semiconductor substrate
10, a conductive member that penetrates the insulating film 70 and
is electrically connected to the intermediate conductive member 61
may be formed of the same material as the contact plug 91. For
example, a contact plug (electrode) 92 of tungsten (W) and the
like, which penetrates the insulating film 70 and is electrically
connected to the intermediate conductive member 61, is provided.
For example, wiring 100 of aluminum (Al) and the like, which is
provided on a surface of the insulating film 70, brings the contact
plug 91 and the contact plug 92 into electrical connection to each
other. In this way, the external connection electrode 33 of the
resonator can be electrically connected to the MOS field-effect
transistor.
[0040] By thus using, as a connecting member for the functional
element, a conductive member formed of the same material as a
connecting member for the semiconductor circuit element, the
material of the connecting member for the functional element can
double as the material of the connecting member for the
high-performance semiconductor circuit element. Also, as the cavity
is formed in the trench of the semiconductor substrate 10, a layer
structure formed on the semiconductor substrate 10 is planarized,
and formation of a wiring layer is made easy. Furthermore, the
height of an upper end of the contact plug 92 for the functional
element can be aligned with the height of an upper end of the
contact plug 91 for the semiconductor circuit element, and these
contact plugs can be brought into connection to each other by
wiring provided on the same layer.
[0041] A description is now given of a method of manufacturing the
MEMS device shown in FIG. 1.
[0042] FIGS. 2A to 3C are cross-sectional views pertaining to
manufacturing processes of the MEMS device according to the
embodiment of the invention. First, for example, by providing a
resist 11 using a photolithography technique and applying dry
etching to a part of the main surface of the semiconductor
substrate 10 constructed from a silicon monocrystal and the like, a
deep trench 10a is formed in the first region of the main surface
of the semiconductor substrate 10 as shown in FIG. 2A. Thereafter,
the resist 11 is removed.
[0043] Next, as shown in FIG. 2B, the insulating film 20 is formed
on a bottom surface of the trench of the semiconductor substrate
10. For example, the insulating film 20 includes the insulating
film 21 of silicon dioxide (SiO.sub.2) and the insulating film 22
of silicon nitride (SiN). The insulating film 22 of silicon nitride
(SiN) withstands wet etching (release etching) for removing a
later-described sacrificial film in the cavity.
[0044] Also, for example, polysilicon that has been doped with
impurities and has electrical conductivity is formed on the bottom
surface of the trench of the semiconductor substrate 10 via the
insulating film 20, and patterning is applied through dry etching
that uses a resist. Consequently, the lower electrode 31 of the
resonator is formed. Furthermore, after forming a gap sacrificial
film 23 on the lower electrode 31, for example, polysilicon that
has electrical conductivity is formed, and patterning is applied
through dry etching that uses a resist. Consequently, the upper
electrode 32 and the external connection electrode 33 of the
resonator and the wall portion 34 are formed. Thereafter, the gap
sacrificial film 23 is removed through wet etching.
[0045] In this way, the resonator including the external connection
electrode, as well as the wall portion 34, which is the structural
member that forms the cavity surrounding the resonator, is formed
on the bottom surface of the trench of the semiconductor substrate
10 via the insulating film 20. It should be noted that the wall
portion 34 may be provided directly on the bottom surface of the
trench of the semiconductor substrate 10. Also, in a case where a
substrate with high insulating properties, such as a substrate of
glass, ceramics, resin, or the like, is used, the lower electrode
31 to the external connection electrode 33 may be provided directly
on the substrate.
[0046] Next, after an insulating film of silicon dioxide
(SiO.sub.2) and the like is deposited, using a plasma CVD
technique, on the surface of the semiconductor substrate 10 on
which the resonator and the like are formed, the insulating film of
silicon dioxide (SiO.sub.2) and the like is polished by CMP
(Chemical Mechanical Polishing), and patterning is applied through
etching. As a result, as shown in FIG. 2C, the insulating film 41
of silicon dioxide (SiO.sub.2) and the like is formed so as to
surround a predetermined region 33a on a surface of the external
connection electrode 33, and an insulating film 42 of silicon
dioxide (SiO.sub.2) and the like is formed as a sacrificial film in
the cavity.
[0047] Next, after an insulating film of silicon nitride (SiN) and
the like is formed on the surface of the semiconductor substrate 10
on which the insulating films 41 and 42 and the like are formed,
patterning is applied to the insulating film of silicon nitride
(SiN) and the like through dry etching that uses a resist. As a
result, as shown in FIG. 3A, the insulating film 51 of silicon
nitride (SiN) and the like is formed. The insulating film 51 covers
the insulating film 41 at the first surface of the external
connection electrode 33, and covers a part of the cavity.
[0048] Also, after a polysilicon film that has electrical
conductivity is formed on the surface of the semiconductor
substrate 10 on which the insulating film 51 and the like are
formed, patterning is applied to the polysilicon film through dry
etching that uses a resist. As a result, as shown in FIG. 3A, the
first lid portion 50 including the insulating film 51 and the
polysilicon film 52 is formed. The opening 50a is formed in the
first lid portion 50. The part of the first lid portion 50 other
than the opening 50a covers the cavity. Here, a part of the
polysilicon film 52 is provided in the predetermined region of the
first surface of the external connection electrode 33, and is
electrically connected to the external connection electrode 33.
[0049] Next, on the surface of the semiconductor substrate 10 on
which the first lid portion 50 and the like are formed, for
example, grooves are formed, an insulating film of silicon dioxide
(SiO.sub.2) and the like is formed, and insulating film
planarization is applied. Thereafter, for example, a MOS
field-effect transistor (MOSFET) is formed as a semiconductor
circuit element in the second region of the semiconductor substrate
10 as shown in FIG. 3B.
[0050] That is to say, the gate electrode 83 is formed on the
semiconductor substrate 10 via the gate insulating film, and the
impurity diffusion regions 81 and 82 that serve as the source and
the drain are formed inside the semiconductor substrate 10 on both
sides of the gate electrode 83. Also, insulating side walls may be
formed on side walls of the gate insulating film and the gate
electrode 83. Furthermore, an insulating film of a predetermined
thickness may be formed in a region surrounding the insulating side
walls.
[0051] In addition, a resist 24 that has an opening 24a in a
position corresponding to the opening 50a of the first lid portion
is provided, using a photolithography technique, on the surface of
the semiconductor substrate 10 on which the MOS field-effect
transistor and the like are formed. Furthermore, the sacrificial
film in the cavity is removed through wet etching (release etching)
that uses hydrofluoric acid and the like as an etchant. Thereafter,
the resist 24 is removed using MCP and the like.
[0052] Next, metal, such as aluminum (Al), is deposited on the
surface of the first lid portion 50 through sputtering (a
high-vacuum film formation technique) in a vacuum chamber, and
patterning is applied to the deposited metallic layer through dry
etching that uses a resist. In this way, as shown in FIG. 3C, the
second lid portion 60 is formed on the surface of the first lid
portion 50 by metal, such as aluminum (Al).
[0053] The second lid portion 60 includes the intermediate
conductive member 61 that is electrically connected to a
predetermined region of the external connection electrode 33 via
the polysilicon film 52, and the sealing portion 62 that seals the
opening 50a of the first lid portion. Also, the opening 60a, which
penetrates the second lid portion 60 and the insulating film 51 and
extends to the insulating film 41, is formed through dry etching
that uses a resist.
[0054] Next, as shown in FIG. 1, the insulating film 70 of silicon
dioxide (SiO.sub.2), BPSG, or the like is formed on the surface of
the second lid portion 60. The insulating film 70 is in contact
with the insulating film 41 or 51, and insulates the intermediate
conductive member 61 of the second lid portion 60 from the sealing
portion 62. The insulating film 70 may constitute the
insulating/isolating portion by penetrating the second lid portion
60 and the insulating film 51 and coming into contact with the
insulating film 41 as shown in FIG. 1.
[0055] The insulating film 70 may extend to the second region of
the semiconductor substrate 10 in which the MOS field-effect
transistor is formed. In this case, the contact plugs 91 and 92 of
tungsten (W) and the like are simultaneously formed. The contact
plug 91 penetrates the insulating film 70 and is electrically
connected to the MOS field-effect transistor, whereas the contact
plug 92 penetrates the insulating film 70 and is electrically
connected to the intermediate conductive member 61. Thereafter, the
contact plugs 91 and 92 are brought into electrical connection to
each other by forming the wiring 100 of aluminum (Al) and the like
on the surface of the insulating film 70.
[0056] FIGS. 4A and 4B are enlarged cross-sectional views showing a
part of the MEMS device in major manufacturing processes. FIG. 4A
shows a part of the MEMS device in the release etching process. The
following describes a case in which the insulating film 41 and the
insulating film 51 are formed of silicon dioxide (SiO.sub.2) and
silicon nitride (SiN), respectively. In this case, hydrofluoric
acid can be used as an etchant in the release etching process.
While hydrofluoric acid dissolves and corrodes silicon dioxide
(SiO.sub.2), it is difficult to dissolve silicon nitride (SiN) with
hydrofluoric acid.
[0057] Therefore, by covering the insulating film 41 of silicon
dioxide (SiO.sub.2) with the insulating film 51 of silicon nitride
(SiN), which has a high resistance to etching, on the external
connection electrode 33 as shown in FIG. 4A, the insulating film 41
can be protected from the etchant, and a degree of vacuum can be
prevented from decreasing due to discharge of gas, such as water
vapor, from silicon dioxide (SiO.sub.2).
[0058] Also, the insulating film 41 plays a role in guarding the
external connection electrode 33 and the polysilicon film 52 such
that electrical connection between the external connection
electrode 33 and the polysilicon film 52 is not damaged by release
etching. For this reason, the insulating film 41 needs to have a
reasonable size. In view of this, the size of the insulating film.
41 can be reduced by protecting the insulating film 41 from the
etchant with the insulating film 51.
[0059] FIG. 4B shows a part of the MEMS device in a process for
applying dry etching to aluminum and the like. As shown in FIG. 4B,
the opening 60a that penetrates the second lid portion 60 and the
insulating film 51 and extends to the insulating film 41 is formed
through dry etching. In this dry etching process, the insulating
film 51 of silicon nitride (SiN) is easy to etch, whereas the
insulating film 41 of silicon dioxide (SiO.sub.2) is difficult to
etch. Therefore, the insulating film 41 can protect the external
connection electrode 33 by preventing application of dry etching to
the external connection electrode 33.
[0060] While the above-described embodiment has discussed a MEMS
device with a cavity that is formed in a deep trench of a
semiconductor substrate, the invention is by no means limited to
the above-described embodiment. For example, the invention can be
utilized in a MEMS device with a cavity that is formed in a shallow
trench of a substrate or on the substrate, and can be modified in
many ways by a person of ordinary skill in the art within the
technical ideas of the invention.
[0061] The entire disclosure of Japanese Patent Application No.
2014-048448, filed Mar. 12, 2014 is expressly incorporated by
reference herein.
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